Brand, documents and smart cards authentication and security are important applications in today's information Era. Tagging brand product to prevent forging and copying, marking money bills, credit cards, Passports and ID cards are all examples for the need for sophisticated security and authentication measures that are difficult to imitate or forge. Watermarks, holograms, special materials and marks are all examples for such measures, currently employed in bills, credit cards and ID documents.
The primary requirements for such measures are that it would be extremely difficult to copy or forge them and that their realization is relatively inexpensive. As can be expected both demands are, to some extent, contradictory.
Currently available solutions are based on RFID chips, visible/invisible micro-printed patterns and holograms. These solutions suffers from several inherent drawbacks such as partial security, high cost, large dimensions (in particular RFID and holograms), privacy issues (RFID), and lack of flexibility.
G. Antes (U.S. Pat. No. 5,101,184) proposed using multiple diffraction elements consisting of sets of surface gratings and an appropriate apparatus for authentication. This invention, however, is limited to passive diffraction elements which can be analyzed and counterfeited using relatively simple and inexpensive apparatus.